[Mgb-v8] Oops

[Paul Hunt]

Whoa.  For a start another main reason for PCV is to remove condensation 
from the crankcase.  In cold weather on short journeys this can develop to a 
thick creamy emulsion and cause internal corrosion.

Even more of a Whoa is that inlet manifold vacuum is *not* applied to the 
crankcase directly.  The breather port on SU carbs is situated between the 
throttle butterfly and the piston.  Without going into the details the 
effect of that is to apply a relatively constant vacuum of only a couple if 
inches Hg. - a by-product of the constant-depression feature of the carbs - 
not full manifold vacuum which can be as high as 25 in.Hg.  Before SUs had 
the port, and with non constant-depression carbs, a PCV valve is fitted 
which *is* plumbed into the inlet manifold, but which again reduces manifold 
vacuum to just a couple of in.Hg.  It's when this valve sticks or the 
diaphragm ruptures that full inlet manifold vacuum *can* be applied to the 
crankcase, and that usually causes high oil consumption.

PaulH.

----- Original Message ----- 
From: "Greg A Myer" <motorhead45 at juno.com>
To: <mgb-v8 at autox.team.net>
Sent: Thursday, September 24, 2009 3:56 PM
Subject: [Mgb-v8] Oops


> That didn't work.
> Let's try it again.
> http://www.britishv8.org/British-V8-Current-Issue.htm
>
>    That should be better.
>                                   Greg